1. Field of the Invention
The present invention relates generally to computer internetworking. More particularly, the present invention is directed to a resilient internetwork connection between frame relay networks.
2. Related Art
Frame relay (FR) end user-systems or networks are interconnected by a separate data network. User-network interfaces link each FR end user-system to the data network. In commercial applications, these user-network interfaces include gateway switches provided in nodes near business premises for switching data between a FR network and the interconnecting data network. Greater volumes of vital communications traffic are now sought to be sent over long-distances between interconnected FR systems. Sound network-to-network interconnections which transfer data reliably and quickly from end-to-end without error is increasingly important.
Unfortunately, a number of problems can occur resulting in network-to-network failure. Physical trunk failures, such as a fiber cut, can halt communication between frame relay networks. For example, lightning, backhoes, train derailment, trawler nets, and shark attacks have been reported to have severed or impaired fiber connectivity. See, Grover, W., PhD., "Distributed Restoration of the Transport Network," p 337. Even more likely culprits for internetwork connection error are hardware and/or software created problems such as network-interface card (NIC) failure or human error in software loading.
Self-healing networks, such as asynchronous transfer mode (ATM) networks, can restore communication to overcome some types of failure. Restoration algorithms and protocols allow the self-healing network to re-route data within the self-healing network to avoid a faulty switch, node, or trunk. Even failures at a physical user-network interface connected to the self-healing network can be detected. A communication path within the self-healing network can be restored by switching to a pre-configured back-up path through the self-healing network.
Unfortunately, such resiliency of a self-healing network is limited to an internal response within the self-healing network. Without communication from the self-healing network, end-user systems remain unaware of a detected failure. Failures at the user-network interface are especially troublesome. For example, a broken physical interface linking an end user system and self-healing network will be detected and responded to by the resilient network. The ignorant end-user system, however, will continue to try to send and receive data through the failed physical interface. In this case, the Network-Network Interface (NNI) between the end-user network and the self-healing network is not resilient.
This problem is especially acute between interconnected frame relay networks. Frame Relay is only specified as a User-to-Network Interface (UNI) protocol. There is no standard protocol specified between a FR network and a self-healing network which allows a Network-Network Interface (NNI) to automatically detect a single point failure such as failed physical interface (or link). End-to-end performance suffers as the NNI cannot re-route traffic over non-failed or pre-configured back-up link(s). Thus, the lack of NNI resiliency prevents the interconnection of frame relay networks with end-to-end reliability which is not vulnerable to a single point failure.
What is needed then is a resilient interconnection from end-to-end between frame relay networks. A resilient NNI is needed which can re-route traffic to avoid a failed physical interface or link. For FR networks interconnected by a self-healing network, a standard protocol is needed which allows a NNI to automatically respond to physical interface failures detected by the self-healing network.